Definition of primary treatment in English:

noun

Five out of seven sewage treatment facilities in the Greater Vancouver Regional District provide primary treatment of sewage.

Most Canadian cities, especially those on the west coast, provide only primary treatment to sewage.

At the time many mills did not have primary treatment for mill effluents (for example, the use of a settling pond) and fewer still had secondary treatment ponds, which used aerobics to reduce drastically the pollution risk.